Air horn



Dec. 7, 1937. o. H. EKMAN AIR HORN 3 Sheets-Sheet l Filed 001;. 51, 1935Dec. 7, 1937. Q L N 2,101,385

I AIR HORN Filed Oct. 31, 1935 Sheets-Sheet 2 Dec. 7, 1937. Q I, H KMAN2,101,385

' AIR HORN Filed 001;. 51, 1935 3 Sheets-Sheet 3 Patented Dec. 7, 1937UNITED STATES PATENT OFFHCE AIR HORN lof Ingemar Harald Ekman,Stockholm,

Sweden 11 Claims.

This invention relates to air horns for producing strong characteristictones, as for fire alarm purposes, or for use in connection with specialcars to be driven at a high speed. More particularly, the inventionrelates to that kind of horns in which the sound is produced by means ofcompressed air expelled from a chamber at certain definite intervals. Asa rule, the compressed air is generated by means of a blade wheelrevolving at a high speed inside a cylindrical wall provided with aseries of ports alternately opened and closed during the rotation of theblade wheel. To control the opening and closing of said ports there isprovided either a separate slide valve having a corresponding series ofopenings or a circumferential flange on the blade wheel formed with asimilar series of openings. By this means, a successive opening andclosing of the ports in the cylindrical wall will be obtained, each portbeing successively opened to its full extent and immediately thereaftersuccessively closed, so that the progress of the opening and closing ofthe ports may be represented by a, substantially, sinusoidal curve. Inthis way, however, it is impos- 5 sible to obtain atone which issufiiciently sharp for many purposes. In order to obtain such anexceedingly sharp tone, the opening and closing periods should be asshort as possible as compared with the entire uncovered period,preferably momentary, so that in a graphical representation, the saidsinusoidal curve will be replaced by a rectangular figure. In this case,the area representing the work done will be correspondingly larger thanthat obtained in connection with a sinusoidal curve.

The present invention has for its object to provide a horn which enablesa more rapid opening and closing of the sound ports leading from thechamber containing the compressed air than that obtainable in connectionwith a horn having a revolving blade wheel.

The invention is characterized, chiefly, by the fact that the outletport or ports of the chamber containing the compressed air is or areprovided with one or more valves controlled, in part, by a magnetic orother retaining power decreasing with increased opening of the valve,which tends to keep the valve or valves in closed position, and in part,by a counter-power alternately brought into and out of action oralternately increasing and decreasing which tends to open the valve orvalves, the strength or the highest strength of this counter-power beingsufficient to overcome the retaining power. Thus, the counter-power,which hereinafter will be termed the opening power,

will open the valve at a speed which is accelerated accordingly as the.retaining power decreases, for instance, by the square on the distance,and, should the valve during the opening period exceed the working rangeof the retaining power, said opening power will be further increased dueto the fact that the opening power need no longer overcome any retainingpower and may, consequently, yield more work. In the said lastmentionedcase it is necessary, in order again to bring the opened valve withinthe reach of the retaining power, when the opening power ceases or isdecreased sufficiently, either temporarily to increase the retainingpower or to impart an initial movement to the valve by the action ofgravity, or by means of springs or the like. The valve is then broughtto its closed position under the action of the retaining power, i. e. ata speed accelerating accordingly as the valve approaches its closedposition, as for instance, inversely as the square on the distance tothe closed position. It is thus evident that the invention allows theattainment in both directions of the same acceleration at least as thatappearing in case of the magnetic attraction. Any similar eifect cannotbe obtained with the use of a diaphragm or a spring as a counter-powercounter-acting a magnetic attraction, because the magnetic attractionwould be counteracted by the unavoidable tension of the diaphragm orspring. The opening power may be of different kind; it may, forinstance, be produced electromagnetically or pneumatically, or by meansof some merely mechanical means.

With the use of a magnet or an electro-magnet for the production of theretaining power, the amount of the opening power required may be variedarbitrarily by varying the strength of field of the magnet or thestrength of current of the electro-magnet. and it is thus possible toobtain, in a simple way, an exact adjustment of the working effect to bereleased in the one instance or the other. By thus varying the retainingpower, the frequency of the cutting in and cutting out of the openingpower and thus also the frequency of the sound emission may be varied.Another advantage gained by the apparatus according to the inventioninvolves that the apparatus operates in a practically constant magneticfield, so that the movements will not be retarded by the action of suchlarge counter-electromotive forces which act to delay, or suppress, theacceleration of the movements of the armature of an electric frequencyapparatus of the hammer type or of some other type, especially at higherfrequencies.

In the accompanying drawings, Fig. 1 is a secmatic way. Fig. 2 shows amodified form of the apparatus shown in Fig. 1. Fig. 3 is a section of ahorn of a modified design, but still constructed so that the openingpower is pneumatic. Fig. 4 is a section of a horn provided with twovalves. Fig. 5 is a section on the line V,V of Fig. 1; Fig. 6 is asection on the line VIVI of Fig. 3; Fig. '7 is a section on the lineVII-VII of Fig. 4; Fig. 8 is a perspective view of elements of thedevice of Fig. 3; Fig. 9 is a perspective view of the device of Fig. 4with the horn and the valves removed.

With reference to Figs. 1 and 5, the numeral I indicates a chambercommunicating through an opening 2 with a receptacle 3 containingcompressed air. Leading from the chamber I to a horn is an outletpassage 5 controlled by a valve 6. Said valve 6 comprises avery elasticdiaphragm, preferably consisting of an elastic steel blade clamped atits one end, as shown at 1, and so arranged as to form an armature of anelectromagnet 8 the core of which 9 forms a pole piece against which thefree end of the diaphragm B bears when in closed position. The circuitof the electromagnet contains, preferably, a variable resistance I 0 inseries with a source of current II. The size of the opening 2 betweenthe chamber I and the receptacle 3 may be varied by means of a screw I2.The operation is as follows:

Let it be assumed that the chamber I contains air of atmosphericpressure and that the valve 6 is closed, as shown in the drawings.Compressed air will enter the chamber I from the receptacle 3 throughopening 2, subjecting the diaphragm valve 6 to an increasing pressurewhich tends to lift the valve away from the pole piece 9.

As soon as this pressure overcomes the suitably adjusted attractionexerted by the magnet 8, the valve 6 will be moved to its open positionby a power increasing according as the attraction of the magnetdecreases, that is to say, at a rapidly accelerating speed. A quantityof compressed air is now expelled through the horn, reducing thepressure in the chamber I and allowing the valve 6 to be restored to itsclosed position by the attraction exerted by the magnet 2. As soon as amaximum pressure is attained in chamber I, the operation described willbe repeated.

The restoring of the diaphragm 6 to its closed position may becontrolled either by controlling the circuit of the electromagnet 8 orby adjusting the size of the opening 2 with a view to obtaining asufiicientperiod of rest in the emission of the sound. By a regulationof the circuit of the magnet with a view to increasing the strength offield, a higher air pressure must be produced below the diaphragm beforethe latter starts its opening movement. This results in a more rapidopening movement of the diaphragm 6, that is to say, a more rapidexpelling of the air into the horn, as well as an expelling of a largerquantity of air per unit of time during the first part of the expellingperiod. The expelled air will have a steeper wave front and the airparticles producing the sound will have a larger kinetic force, that isto say, I will obtain a tone of a higher intensity than that obtainableas result of the expelling of air of a lower pressure and moresuccessively.

The air contained in the passage 5 above the diaphragm valve 6 is causedto cooperate instantly with the compressed air bel w th diaphragm,inasmuch as the diaphragm, when leaving the pole piece 9, acts on saidair to expel same. At the same time a suitable cushioning of the impactof the diaphragm upon the upper most wall of the passage 5 is secured.

If, for instance, the pole of the magnet 8 facing the diaphragm isassumed to be a north pole, the part of the diaphragm bearing againstthe pole piece 9 will represent a south pole. Of course, I may providein the upper wall of the passage 5 an auxiliary magnet having its northpole facing the diaphragm and so arrange said auxiliary magnet as toallow it to keep the diaphragm away from the magnet 8 during a longerperiod of time in case of large deflections of the diaphragm, that is tosay, in case of an adjustment for a higher pressure of the air in thechamber I. Said action is due to the fact that the diaphragm as a resultof larger deflections will enter a more and more strong field asproduced by said auxiliary magnet.

In order that the device may operate in the desired way it is anindispensable condition that the retaining power tending to keep thevalve in its closed position, decreases with increasing opening movementof. the valve, as otherwise the diaphragm would adjust itself into anequilibrium or vibrate about an equilibrium between closed andcompletely open position.

In Fig. 2 is shown a modified form of the outlet passage 25 leading fromthe pressure chamber M to the horn 24. Herefthe outlet passage 25 isconstricted symmetrically from, its top and bottom walls at its mouthopening into the born 24, as shown at 26, thereby allowing the aircolumn in the horn to be acted upon centrally by the blow of pressure asexerted by the outflowing air.

In Figs. 3, 6 and 8 is shown an embodiment, in which the armature of theretaining magnet 38 which forms a valve between the pressure chamber 3|and the horn 34, is shaped as a conical surface 36. The core 39 of theretaining magnet 38 is cup-shaped and surrounds the pressure chamber 3I,openings 32 being provided in the bottom of the cup-shaped core in orderto allow communication with the receptacle for the compressed air 33. Atits top or mouth the core 39 is formed with a seat 31 to be engaged bythe conical valve 36. The horn 34 is connected at its rear end to anannular space 35 surrounding the uppermost part of the valve 36. Theoperation is similar to that above described. In order to guide thevalve 36 to its proper position into engagement with the seat 31, whenattracted by the magnet 38, there is provided a spring 40 attached tothe apex of the conical valve 36. The conical valve 36 may be providedwith apertures or projections, if required, to prevent the valve frombeing locked against movement.

It is to be noted that the single diaphragm armature of the retainingmagnet may be replaced by a plurality of armature elements'or diaphragmsacting as valves, this arrangement, however, requires a completesynchronism between the movements of the various armature elements orvalves in order to obtain a pure tone and an efficient cooperation,

A solution of this problem requires the satisfaction of the followingconditions:

There must be a common pressure chamber to produce the opening movementof the diaphragms or valves in order that the pressures acting on theindividual valves shall change synchronously. Each diaphragm or valvemust allow individual adjustment once for all by means of resistancesinserted in the circuit of the electromagnet or, if desired, by usingdiaphragm valves of predetermined tension. There must be a device foreffecting an automatic control of the various valves with relation toeach other, so that any valve when opening may facilitate the opening ofthe other valves. This efiect may be obtained, for instance, by the useof a common retaining magnet circuit for all valves and magnets, so thata reduction of the attractive force will automatically take place, assoon as air is admitted to the 'iron circuit through any valve. Oneembodiment of this type is illustrated in Figs. 4, 7 and 9.

With reference to Fig. 4, the core :39 of the magnet 68 constitutes apressure chamber 4| communicating through apertures, one of which isshown at 42, with a receptacle for compressed air, not shown. Theconnection between the pressure chamber ll and the horn 44 iscontrolled'by two diaphragm valves 46. These valves bear in their closedposition with their free ends upon a pole piece 50 on opposite sides ofa non-magnetic mass 5!, so that in this position a closed magneticcircuit exists which includes the two diaphragm valves 45. If one of thediaphragm valves, say the left one, lifts prior to the other, the airgap thus formed between the pole piece 50 and this diaphragm isintroduced into the magnetic circuit, reducing the attractive force, sothat the magnet cannot keep the other diaphragm attracted, with theresult that also this diaphragm will be released.

What I claim is:

1. A siren having a chamber for receiving a fluid under pressure and anoutlet leading from said chamber, a valve for controlling said outlet,electro-magnetic means for producing a retaining power acting upon thevalve to keep same in closed position, said retaining power being ofsuch a nature as to become reduced with increasing opening of the valve,said chamber having a restricted inlet to allow the fluid to generate inthe chamber, a source of counter-power acting on the valve to open same,said counter-power being of such nature as to be alternately increasedand decreased depending on the closing and opening of the valve, thestrength, or the highest strength, of said counter-power beingsufficient for overcoming the action of the retaining power.

2. A siren having a chamber for receiving a fluid under pressure, saidchamber having a restricted inlet and a large outlet, a valve forcontrolling said outlet, said valve having a large area exposed to theinterior of said chamber toallow the fluid pressure therein to producethe counterpower tending to open the valve, and electro magnetic meansfor producing a retaining power acting upon the valve to keep same inclosed position, said retaining power being of such a nature as tobecome reduced with increasing opening of the valve, the strength, orthe highest strength, of said counter-power being sufficient forovercoming the action of the retaining power.

3. A siren having a chamber for receiving a fluid under pressure, saidchamber having a restricted inlet and a large outlet, a valve forcontrolling said outlet, said valve having a large area exposed to theinterior of said chamber, an electro-magnet for producing a retainingpower ac ing upon the valve to keep same in closed position, and asource of counter-power acting on the valve tending to open said valve,the strength, or the highest strength, of said counter-power beingsufficient for overcoming the action of the retaining power, and meansto vary the section of pas sage of said inlet.

4. A siren having a chamber for receiving a fluid under pressure, saidchamber having a restricted inlet and a large outlet, a diaphragmclamped at its one end for controlling said outlet, an electromagnetcooperating with the free'end of said diaphragm to keep same in closedposition, the diaphragm being exposed between its ends to the interiorof said chamber so as to be subjected to the pressure of the fluidtherein, acting on the diaphragm to open same, the pressure, or thehighest pressure, in said chamber being sufficient to overcome theaction of the retaining power, as exerted by the electromagnet.

5. A siren having a chamber for receiving a fluid under pressure, saidchamber having a restricted inlet and a large outlet passage, means tovary the section of passage of said inlet, an electromagnet arranged inthe wall of said chamber near the mouth of said passage, and a diaphragmvalve of magnetic material clamped in the wall of the chamber at the endof said outlet passage remote from the electromagnet and cooperating atits free end with said electromagnet so as to extend, substantially, inthe longitudinal direction of the outlet passage and being capable ofmoving under the influence of the fluid pressure in the chamber, withits free end, between said electromagnet and the opposite wall of theoutlet passage.

6. A siren having a chamber for receiving a fluid under pressure, saidchamber having a restricted inlet opening and a large outlet passage,means to vary the section of passage of said inlet opening, a hornleading from the mouth of said outlet passage, an electromagnet arrangedin the wall of said chamber near the mouth of said passage, a diaphragmvalve of magnetic material clamped in the wall of the chamber at the endof said passage remote from the electromagnet and cooperating at itsfree end with said electromagnet so as to extend, substantially, in thelongitudinal direction of the outlet passage and being capable of movingunder the influence of the fluid pressure in the chamber, with its freeend, between said electromagnet and the opposite wall of the outletpassage.

7. A siren having a chamber for receiving fluid under pressure, saidchamber having a restricted inlet opening and a large outlet passage,the mouth of said passage being contracted symmetrically from oppositesides. a horn leading from said contracted mouth, an electromagnetarranged in the wall of said chamber near the mouth of said passage, adiaphragm valve of magnetic material clamped in the wall of the chamberat the end of said passage remote from the electromagnet and cooperatingat its free end with said electromagnet so as to extend, substantially,in the longitudinal direction of the outlet passage and being capable ofmoving under the influence of the fluid pressure in the chamber, withits free end, between said electromagnet and the opposite wall of theoutlet passage.

8. A siren having a chamber for receiving a fluid under pressure, saidchamber having a restricted inlet and a large outlet, a conical valve tocontrol said outlet, an electromagnet for closing said valve, an annularcore belonging to said electromagnet, said core having an annularconical seat for said valve, said valve being exposed to the interior ofsaid chamber on its side facing the'electromagnet so as to be opened bythe pressure of the fluid in said chamber.

9. A siren comprising a receptacle for a fluid under pressure, anelectromagnet, a cup-shaped core belonging to said electromagnet, saidcore having openings in its bottom for communication with saidreceptacle, the core forming an annular seat at its open top, a conicalvalve to be brought into engagement with said seat under the action ofthe electromagnet and to be lifted therefrom under the action of thefluid contained in the cup-shaped core, said receptacle forming anannular space above said seat, and a horn leading from said annularspace.

10. A siren having a chamber for receiving a fluid under pressure and anoutlet leading from said chamber, a horn leading from said outlet, aplurality of valves for controlling said outlet, said valves beingexposed to the interior of said chamber so as to be opened by thepressure of the fluid in said chamber, an electromagnet to bring saidvalves to closed position, said valves being so arranged as to formparts of the magnetic circuit of said electromagnet when in their closedor the highest strength, of said fluid pressure being sufficient toovercome the action of the electromagnet, and means to vary the strengthof the electromagnet.

OLOF INGEMAR HARALD EKMAN.

